Reflectors to Improve the
Performance of Solar Collectors (and Windows)

This is a section that looks into using reflectors to improve the
performance of solar thermal collectors (including windows). The section covers:

- Reflector design information (tables)

- An earth-sun simulator you can build too optimize reflector designs

- Some tests of reflectors on actual collectors

- Links to projects using reflectors for
performance improvement

- Some thoughts on using reflectors

A key advantage of reflectors over just adding more collector area is that reflectors add to solar gain without
adding to collector heat losses. A typical
collector operating with a modest sun level of 500 watt/sm under winter
conditions might have an efficiency around 30%, but if you can boost the sun
intensity to 1000 watts/sm with a reflector, the efficiency jumps up to more
than 50%. The heat output goes from (500 w/sm)(0.3) = 150 watts up to
(1000 w/sm)(0.5) = 500 watts -- a 3.3 times increase in heat output! You
would have to more than triple the area of the collector to get this increase.
Granted, this takes a VERY well designed reflector, but you get the idea.

Reflectors might be particularly helpful on passive gain homes that use larger areas of south facing glass for solar gain, but also experience large heat loss through this glass at night. Reflectors could be used to reduce the area of the south glazing while maintaining the same solar gain.

Reflectors are particularly effective in improving vertical collectors (or windows) in the late spring, summer, and early fall when the sun is high in the sky and the solar incidence angle on vertical collectors is high.

This section deals with using flat reflectors to improve the
performance of flat collectors or windows -- it does not deal
concentrating reflectors such as parabolic dishes or
troughs etc. -- see this page for more on
concentrating collectors and reflectors...